We search for industry news, so you don't need to.
Ask the Experts  
Questions Index  ■  Submit a Question  ■  Experts Panel  ■  Join the Panel

November 9, 2016

BGA Component Moisture Exposure

We mistakenly assembled circuit boards using BGA components that were not properly stored. The BGA components had moisture tags that show indication of moisture exposure. All the assemblies passed testing.

Can we now rebake the assemblies to ensure we will not have moisture related failures on these devices?

Should we remove and replace the suspect BGA components?

M. M.

Experts Comments

Any damage that might have been done by processing expired MSDs cannot be reversed by baking the assemblies.  And the fact that the assemblies passed in circuit and functional testing is not proof that there was no damage during reflow. 

One of the most critical facts to understand about the dangers of improperly managing Moisture Sensitive Devices is that the micro-cracking and related defects are difficult to detect.  They are frequently on the underside of the components and typically manifest themselves in the form of field failures two to six months after the fact.

There is no substitute for a comprehensive MSD management process just as there is no substitute for a comprehensive ESD management process.  And lead free processing raises the risk of not having procedures in place even higher.

image
Richard Heimsch
Director
Protean Marketing
Now a director at Protean Marketing, Mr. Heimsch has worked in the electronics industry 25+ years in a wide variety of international sales, marketing and operations roles. Rich spearheads Protean's international business development, specializing in Brand Management and Strategic Communications.

Instead of using heat (a known enemy of electronics) in an attempt to drive off moisture, it may be more advantageous to use a vacuum chamber in order to actively evaporate any residual water. Heating can put undesirable thermal stresses on electronic devices, which can lead to premature failure.

Try using a batch-type plasma cleaning system or other type of vacuum chamber, and pump the chamber down into the several-hundred mTorr range for 15 to 20 minutes (without engaging any plasma or heating, of course.) We find this is usually sufficient to remove residual moisture from electronic components.

Anecdotal of course, but we've had success this way recovering cell phones that have been accidentally dropped into water. The key is to immediately remove the battery from the phone in order to ensure there are no short circuits before the water can be thoroughly removed via this vacuum process.

Whether or not you'll see short- or long-term failures in your components due to moisture exposure depends on many factors: Did any shorts occur while the moisture was actually present? Did the moisture deposit any contaminants (such as salts or acids) that can subsequently cause shorts, corrosion, or delamination? Did the moisture induce any other modes of failure into the component?

A bit of a disclaimer: For mission-critical electronics, such as those used in medical devices, military electronics, or avionics, the safest action is always to replace components which are known to have been exposed to moisture.

image
Scott D. Szymanski
Global Marketing Manager
Nordson MARCH
Mr. Szymanski works to expand strategic alliances, strengthen partnerships with equipment suppliers, and develop future product offerings tailored to the semiconductor market.
NOTE: Mr. Szymanski is no longer working at Nordson MARCH

If the components surpassed allowable moisture exposure limits prior to reflow, which sounds likely, then they may have incurred internal damage during reflow.   Typical moisture-induced defects include micro-cracking or delamination inside the component body, due to excessive pressure exerted by absorbed water molecules during reflow.   There is usually no external evidence that can be detected through visual inspection, X-ray or other standard inspection techniques.

Such defects are often latent; in other words not severe enough to cause immediate failure.  This would explain why the units passed initial testing.  However, out in the field and over time a small crack can propagate into a larger one, suddenly and unexpectedly (think crack in your car's windshield), resulting in intermittent performance issues, early life failure, or diminished long term reliability.

Re-baking the assemblies now will not "undo" any damage that occurred during the initial reflow process. Your safest bet is to replace these components with ones that were stored and monitored properly prior to reflow.  If they are expensive then an alternative would be to send them to a lab for acoustic microscopy.  An acoustic microscope is the only non-destructive way to check inside the component body for cracks and delaminations.  Such an analysis would confirm for sure whether the components need to be replaced.  

image
Mitch DeCaire
Sales Manager (Americas)
Cogiscan, Inc.
Mitch DeCaire, Sales Manager at Cogiscan, has served the electronics manufacturing industry since 1989. His prior experiences include process engineering, business development, and engineering management roles with Nortel Networks, Vansco Electronics, Universal Instruments and Siemens.

When overexposed Moisture-sensitive components go through the solder reflow cycle, the entrapped moisture will turn into steam which can cause internal cracks and delaminations. These internal defects will not necessarily cause an immediate component failure but they can affect their reliability.

Rebaking these assemblies will not fix the problem. To evaluate the risk you could perform some reliability tests on the affected units. The simplest solution is to remove and replace the suspect BGA components with dry ones.

For more information on this topic I invite you to consult the MSD Knowledge base on our web site.

image
Francois Monette
VP Sales & Marketing
Cogiscan
Mr. Monette is one of the co-founders of Cogiscan and leads global sales, business development and marketing. Since 1990, he has held a variety of positions in the electronics manufacturing industry, mostly focused on quality and process engineering.
Baking the assemblies will not fix the parts if they got damaged during reflow. Passing test is not a separation criteria for bad boards from the good boards. Changing the components will involve the usual risk of scrap during rework but do it if the components are suspect and the final product functionality is critical.
image
Georgian Simion
Engineering and Operations Management
Independent Consultant
Georgian Simion is an independent consultant with 20+ years in electronics manufacturing engineering and operations.
Contact me at georgiansimion@yahoo.com.
Submit a Comment

Your Name


Your Email


Company Name


Country


Comments




Authentication

Please type the number displayed into the box. If you receive an error, you may need to refresh the page and resubmit the information.